As one of the victims lay on the road next to the tram getting help from an onlooker, a bystander filmed the scene on their smartphone.

Within hours the footage had found its way onto the social news aggregator site Reddit.

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The Citizen app warns its users to “never approach a crime scene”.

Shortly thereafter, however, the video was removed because, according to a thread on the site purporting to be from the original poster, the alleged perpetrator was described as "an African guy", something the moderator deemed "race baiting".

The incident is one of many troubling spin-offs from the rapid rise of citizens surveilling each other, in a world where there is a smartphone in every pocket and pictures from almost any misdemeanour can be uploaded to sites such as Reddit or LiveLeak, or indeed be streamed real time via apps such as Facebook Live or Periscope.

Those concerns go beyond the unnerving prospect of vigilantes hunting down dark-skinned people based on social media hearsay, or very real questions about a victim's right to privacy.

The use of apps such as Crimestoppers, recently updated in Queensland and Victoria, which allow smartphone users to send details, photos and video of crimes directly to law enforcement, herald an era where any infraction - ranging from the serious felony to the teenager spraying graffiti or even the Mum illegally parked while dropping her kids at school - becomes fair game for fellow citizens.

A screenshot of the Citizen app supplied by the creators.

So do we have a civic duty to dob and, if so, at what point do the downsides become too great?

Joshua Reeves, an assistant professor at Oregon State University whose book Citizen Spies was released in March, sees a disturbing phenomenon emerging, fuelled by a culture of mutual surveillance fostered, most recently, by counter-terrorism programs such as "if it doesn't add up, speak up".

Citizen and apps like it raise questions around ethics and responsibility of bystanders.

"In order for these programs to work, you have to tie snitching to moral and social responsibility, and you have to teach citizens that they are under threat, and that in order to handle that threat appropriately they have to be watchful and suspicious of their fellow citizens," says Reeves.

Reeves doesn't question the value of reporting serious felonies to police. But he does point out that "snitching" has resulted in some truly awful outcomes, such as the 2009 case of a boy set alight because he was thought to have reported a bike theft to police.

Stop snitching T-shirt logo with crosshairs and bullet holes.

In the US, antipathy to tattling has even spawned its own movement. The "stop snitching" campaign features T-shirts with targets, bullet holes and the phrase "snitches get stitches", something Baltimore police countered with their own pro-informant "Keep Talking" campaign.

Indeed, there is a special term for citizens watching other citizens. It's called "lateral surveillance", and a debate on its merits could soon be on the agenda in Australian schools.

A STOPit poster: If you aren't a bystander, what are you?

An app called STOPit, which allows students to anonymously report to staff incidents from bullying and sexual assault to weapons and drugs possession and to upload photo and video evidence, made its Australian debut last October and is currently in six schools across Western Australia, South Australia and New South Wales, with a planned rollout to hundreds of others.

Notably, the app does not allow for a practice adopted in some US schools, where students have been offered money to turn in suspected drug users.

"If someone can be protected from harm through the intervention of these apps, obviously for them it seems positive," says Reeves.

"But I also think there is a dangerous trend underlying this. It is this entrepreneurial ethic of snitching and spying ... if I nark out these kids in school then I can get either petty social benefits, the social gratification from doing the right thing, or I can actually get paid," he says.

Another concern is that the apps may encourage punitive responses to what are really social ills, something dubbed "the punishment economy" by US human rights activist Zachary Norris.

"Instead of tackling systemic and structural issues of poverty and crime, it is so much easier to develop citizen spy programs," says Reeves.

Kevin Macnish, a philosopher at the University of Twente, has experienced the dystopian extreme of surveillance culture first hand, living in West Berlin in the 1970s when East Germany's Stasi secret police were active across the Wall.

"There feels something wrong in surveillance for which there is no consent … there is an element of lack of trust which accompanies being forcefully surveilled," says Macnish, whose book The Ethics of Surveillance was published in July.

"At its height something like one in 62 citizens was believed to be a Stasi informer. The result is just such a low level of trust in society – you're scared of who you can trust, you're scared of who you can turn to. And so you just don't. That obviously has a massive impact on solidarity, and community spirit, and people just getting along with each other," he says.

And while the German Democratic Republic might seem remote from our own liberal democracy, another app targets offences where the temptation to tip off police may, for some, be irresistible.

In April, researchers at the Korea Advanced Institute of Science and Technology unveiled Mobile Roadwatch, an app that allows people to record traffic violations, such as a car running a red light, and report it to police by touching a smartphone screen while they are driving.

Which raises the sticky question of whether, using our smartphones as dashcams, we might all have a duty to dob in people for traffic offences?

"Proportionality should be brought to bear," says Macnish, who argues that minor breaches of the speed limit are very different from, for example, an out-of-control car threatening to kill someone, where a clear moral duty exists to call it in.

Increasingly, however, proportionality in what to report - and indeed which crimes to deal with personally - is being decided by individuals themselves.

Lennon Chang, a Monash University criminologist, studies the emerging phenomenon of netizens – citizens of the net – engaging in vigilante acts, a behaviour he calls "netilantism".

A high profile example of netilantism is Letzgo Hunting, a British group who entrap suspected paedophiles by posing as minors online, before luring suspects to meetings which are filmed, sometimes posted online, and then reported to police.

Such groups have been denounced for interfering with covert police investigations, procuring inadmissible evidence and inadvertently tipping off suspects. In 2013, British man Gary Cleary hanged himself days after being confronted and filmed by Letzgo Hunting.

Comments on the Letzgo Hunting Facebook page about two convicted child sex offenders show the intensity of hatred among the group's followers: "I hope someone takes the law into their own hands [and] kills the bastard," says one.

The possibilities when amateur sleuthing goes public are truly alarming.

"Messages go viral quickly, so you won't be able to set a bar on harm reduction. The damage will keep going, even if you find out the message is fake or they identify the wrong person. There is no way to remedy it," says Chang.

In 2016 Chang published a study that found netilantes were characterised by three traits: high feelings of personal empowerment; a sense that the criminal justice system was ineffective; and a belief their actions would achieve social justice.

A controversial new app, however, suggests there could be something of the netilante in all of us.

Released in March, Citizen retrieves 911 calls and posts details and locations of current police incidents, which are pushed to the phones of users within 400 metres. Users are prompted to film the incident and share footage with other users.

The app's first iteration, released last November and called - in a staggering misstep - Vigilante, was pulled from the App Store after only two days for encouraging, yes, vigilantism. The current, more measured incarnation only covers New York City but there are plans, according to a spokesperson from Citizen, to extend nationally and beyond the US.

Kate Knibbs, a reporter for The Ringer, recorded her personal experience with Citizen in a June article, when the app notified her of a woman being assaulted 300 metres from her apartment.

Knibbs describes feeling "queasy with guilt" as she and her husband debated whether to seek out and assist the victim, despite the app's warning to "never approach a crime scene".

Could such apps promote vigilantism by unwittingly leveraging human empathy?

Macnish is reminded of an example used by the philosopher Peter Singer. You're walking past a shallow pond and see a child drowning. Will you save the child even if your clothes get muddy? Of course. Moral responsibility drives you to act. When the cost of helping is negligible, like donating to famine relief, Singer concludes we must all act.

But Macnish says intervening in a crime is different.

"Taking a child out of the water so they don't drown is clearly helping that person. Involving yourself in an ongoing crime is not necessarily going to help," he says, noting it could also escalate the danger.

Victoria Police are unequivocal. Inspector Graham Higginbotham of the Safer Communities Unit said via email: "We always ask that members of the public prioritise their safety and remove themselves from potentially dangerous situations rather than lingering to film or take photos."

But when it comes to posting crime to the web, the genie may be out of the bottle.

In February a woman was jailed for live-streaming the rape of a 17-year-old girl on Periscope. And in June a BuzzFeed analysis found 45 cases of violent incidents - including murder, torture and child abuse - had streamed on Facebook Live since its debut in December 2015.

"Are we able to control it? Are we able to stop it? ... We won't be able to stop it, the Internet is free," says Chang, who thinks the way forward is to get people to think before they post and to consider the risks.

Interviewed on ABC radio in July, Harvard University's Sam Gregory, director of the Witness program which trains activists in the ethical use of video to promote human rights, said that he wants people to know how to blur faces before uploading videos to YouTube or Snapchat, and that he encourages people not to post videos immediately but to wait for official accounts of an incident so they can challenge them in an informed way.

Perhaps, also, the privacy rights of people being filmed might put brakes on what is posted?

Unfortunately, according to the authors of a 2016 article, that seems unlikely, at least in the US. They concluded that First Amendment free speech rights are likely to trump privacy concerns and that, ultimately, consumers of tools such as Periscope and Facebook Live will "shape the way they are used".

In Australia, privacy and surveillance were in the headlines in July, when a submission to the parliamentary inquiry into students with a disability or special needs in NSW schools pushed for CCTV to be introduced into the classroom to protect children from abuse by teachers, aides and other pupils.

The move was supported by University of Newcastle academic David Roy on the grounds that it could provide evidence to confirm or refute abuse allegations, but was roundly rejected by the NSW Teachers' Federation as a breach of "basic privacy principles".

Another study, however, published back in 2006, raises the possibility of a silver lining to the explosion of surveillance.

The study took place in a university coffee room. The researchers stuck a picture above the honesty box where staff put money for drinks, and alternated it each week. One week the picture would be flowers and the next a photo of two eyes staring at the viewer. Staff parted with significantly more dosh in "eye weeks" compared to "flower weeks", prompting the experimenters to speculate we may be hard-wired to behave better when watched.

Could all this surveillance, then, be making us better people?

Macnish is not so sure.

"I think there is a concern that [being surveilled] becomes the reason we behave. There is a certain infantilising aspect, if the only reason we're behaving well is because we think somebody is watching us," he says.

"Why not put CCTV everywhere ... why not put CCTV in the home as well?"

Live-streaming technologies, of course, mean smartphones could become a frightening proxy for CCTV in every home, shareable with the world. Big Brother could be in the hands of your little brother.

Chang's take is that, ultimately, using the eyes and ears of citizens in the fight against crime is a good thing.

"We should involve citizens in policing, but be careful not to make the citizens civilian police ... that should be a clear line."